The door lock which is extensively used at present is constituted such that the door is locked if the push knob protruding from the centre of the door handle is pushed in from the interior of the room. However, such a door lock can be easily unlocked by means of an approximately similar key or a metal piece. Furthermore, such a door lock can be easily unlocked by means of an ID card or a name card.
Therefore, when a house wife is staying alone in an apartment and the like, or family members are sleeping during the night with the door lock locked, an unpermitted intruder can easily intrude into the apartment after unlocking the door lock in an easy manner, thereby giving rise to numerous cases of slaughters and other accidents.
An example of such a conventional door lock is disclosed in Korean Utility Model Registration No. 31297 (entitled: Door Lock having a Security Device) granted to the present applicant. The object of the prior art door lock is similar to that of the present invention, but its constitution is quite different from that of the existing door locks. Further, the prior art lock has many problematic features, such as, it occupies too much installation area, and it can not be installed at the position of an existing door lock after removal of it, thereby making it difficult to expect a practical usefullness from this door lock of the prior art.
With reference to the Figures, those parts of the door lock of the present invention which are conventionally known will be described below.
That is, a runner 60 which is coupled with a cylinder 50 at its lower portion and is coupled with a lock plate 62 at its upper portion is installed to a case 30, while its left and right sides are respectively coupled with an outer rotating tube 11 and a movable pipe 40. The outer rotating tube 11 and the movable pipe 40 are respectively coupled with an outer handle 10 and an inner handle 20, while a push knob 48 is slidably inserted into the movable pipe 40. A shaft 27 which is coupled with the push knob 48 at one of its ends is provided with two leading ends 28,29 at another of its ends is installed within the movable pipe 40, while the leading end 29 of the two leading ends extends through the runner 60 installed within the case 30 to an elastic support plate 12 located at the end of the rotating tube 11.
The conventional door lock constituted as described above is further constituted such that a latch 51 elastically supported by means of a spring within the cylinder 50 is engaged with a latch plate (not shown). Under this condition, if the outer and inner handles 10,20 are turned, then the arcuate projections 13,14 of the end of the rotating tube 11 and the arcuate projection 41 of the end of the movable pipe 40 will push the runner 60 upwardly to elevate it as shown in FIGS. 8A and 8B, while the latch 51 engaged with the lower portion thereof is elevated to depart from the latch plate, thereby opening the door. Meanwhile, the operation of locking the door by pushing the push knob 48 is carried out in the manner described below. Upon pushing the push knob 48, the shaft 27 is moved (refer to FIG. 11), in such a manner that the leading end 29 pushes the elastic support piece 12, and that the leading end 28 is inserted into a groove 16 located at the upper portion of the outer rotating tube 11 to prevent the rotation of the outer rotating tube 11. Here, the sliding face 45 of the shaft 27 moves pushing upwardly the lock plate 62 which is elastically installed to the runner 60 by means of a spring 64, while, at the moment sliding face 45 is pushed past the lock plate 62, the lock plate 62 Is restored to the original position due to the force of the spring 64, and a latching face 46 is engaged with the lock plate 62, thereby forming a locked state.
If an unlocking is desired, then the inner handle 20 should be turned, so that the arcuate projection 41 of the leading end of the movable pipe 40 should push up the runner 60, and that the lock plate 62 should be released from the latching face 46 of the shaft 27, thereby restoring the shaft 27 to the original position through the function of the elastic support plate 12 to open the door.
On the other hand, if the outer handle 10 is turned without using the inner handle, the leading end 28 of the shaft 27 is inserted into the groove 16 of the leading end of the outer rotating tube 11 to prevent the rotation of the outer rotating tube 11, and therefore, the arcuate projections 13,14 can not push up the runner 60, so that the door can not be opened.
However, if the key is used as shown in FIG. 8C, although the outer rotating tube 11 is not rotated, an inner rotating tube 15 is rotated owing to the action of the key, so that only the arcuate projection 14 should be rotated to push up the runner 60, thereby releasing the lock plate 62 from the latching face 46 to open the door.
Further, such a door lock can be opened by pushing the latch into the interior of the cylinder 50 through the use of a knife and the like.
Therefore, when a housewife is staying in an apartment and the like with the door locked, or when members of a family are sleeping in night with the door locked, an unpermitted intruder can open the door by means of a corresponding key, a similar key, or by moving the latch through the use of even a knife or a name card.